Transport packing made of plastic and method for the manufacture of a transport packing

ABSTRACT

Transport packings made of plastic are usually manufactured as stable hollow bodies and serve to transport fluids. Due to electrostatic charges building up on the plastic bodies, electrical charges frequently arise, which represent an explosion risk. In order to exclude such risks, the plastic packing includes electrically conductive polymers. These polymers may be applied as paint to the outside of the plastic packing.

CROSS-REFERENCES TO RELATED APPLICATIONS

[0001] This application claims the benefit of prior filed provisional application, Appl. No. 60/279,872, filed Mar. 29, 2001, pursuant to 35 U.S.C. 119(e), the subject matter of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] The present invention relates, in general, to a transport packing made of plastic and to a method for the manufacture of a transport packing.

[0003] Transport packings made of plastic are known in a variety of embodiments and have proved their worth. One problem area is caused by the packing of ignitable materials and their storage in areas subject to the risk of explosion. Plastic packings can lead to a threat due to electrostatic discharge on their surfaces. Accordingly, it is specified in the Guideline “Static Electricity” ZH1/200 from BG Chemie, Section 7.1.1.4, for example, that in an explosion zone 1 for substances of Explosion Group II a, dischargeable surfaces shall not exceed 100 cm2. Electrostatically-conductive parts, including conductive fluids, i.e. those not capable of being charged up, are therefore to be earthed.

[0004] In addition to this, if it is intended that combustible fluids in transport packagings made of plastic are to be handled above their lower explosion point, then it is to be assumed that the requirement of avoidance of sources of ignition in zone 0 is to be fulfilled on the outer casing of the container. For substances of Explosion Group II a, unshielded chargeable surfaces must not then exceed 25 cm2.

[0005] In order to meet these requirements, closed metallic external containers have been proposed, which entirely encase the plastic containers and therefore allow for sufficient earthing. This has the disadvantage, however, that the degree of filling of the container is no longer visible from the outside.

[0006] In addition to this, an extendible sack or bag with conductive material has been proposed, which can be laid around the plastic container. Such circumferential packing types are, however, expensive, and awkward to handle. In addition, it is difficult to guarantee that the chargeable surfaces with extendible sacks or bags of this nature will with certainty not exceed an area of, for example, 100 cm2.

[0007] Plastic packagings have also been proposed which are arranged in a metal cage. The fields of these metal cages lie, for example, below 100 cm2, and the filling cap is formed in a conductive manner by means of a copper/zinc sintering method. Such cages, however, essentially share the disadvantages of the extendible sack or bag described heretofore.

[0008] Finally, it has been proposed that the plastic containers be rendered electrically conductive by means of soot particles. An adequate admixture of soot, however, leads to the plastic container no longer being translucent, and the filling level therefore no longer being easily identifiable from the outside. In addition, the pigments introduced reduce the service life of the containers and, especially in drop tests, lead to the tearing of the container at the bonding seam.

[0009] It would therefore be desirable and advantageous to provide an improved transport packing which obviates prior art shortcomings and is suitable for use in areas subject to a risk of explosion.

SUMMARY OF THE INVENTION

[0010] According to one aspect of the present invention, a transport packing includes a body made of plastic and including an electrically conductive polymer.

[0011] Electrically conductive polymers are marketed today, for example, as admixtures in powder form, which can be added to the plastics. This makes it possible for plastic packagings to be manufactured of which the surfaces feature high conductivity. For preference, the specific resistance lies below 10⁶ Ohm×meter. This leads to the situation in which the plastic packings no longer need to be surrounded with metal grilles or nets, and can also be manufactured very economically even for areas subject to the risk of explosion.

[0012] It is of advantage if the plastic packing is a stable hollow body. Hollow bodies make it possible for containers to be manufactured in a simple manner, which are well-suited for the transport of fluids, for example. Such containers are used in large numbers for the transport and storage of substances subject to the risk of explosion or combustible substances.

[0013] The invention relates in particular to hollow bodies which have a volume of more than 450 liters. These are, as a rule, 1,000 liter plastic containers, which, due to the use of the electrically conductive polymers, contain a special arrangement to avoid electrostatic ignition risks in areas subject to the risk of explosion of Zone 1, Group II a.

[0014] In an advantageous manner such transport packings are made of polyethylene. In this context, mention is to be made in particular of HDPE.

[0015] In a simple manufacturing variant, these plastic packings are blown from an extruded hose section, whereby the hose is pressed together at the separation points. As a result, seam points are created, which are particularly subject to risk with regard to strength. The invention relates in particular to plastic packings which includes a seam point, since the electrically conductive polymers only reduce the strength at the seam points to an insubstantial degree.

[0016] It is of particular advantage if the polymers are applied as a paint to the plastic packing. This allows for two pure polymer materials to be bonded to one another in the seam area, without polymers occurring in this area which could impair the strength of the seam point. The paint is to advantage not applied to the finished plastic container until after the formation of the seam point.

[0017] A paint coating of this nature can also be applied on the inside of the plastic packing as well as on the outside. In the case of containers in particular, it is proposed that the polymers be applied on the outside of the plastic packing. This leads to the situation that the charge on the outside of the packing is conducted away, and facilitates the provision of the electrostatically conductive layer with an earthing arrangement.

[0018] The polymers do not necessarily have to be applied as a continuous uninterrupted paint coating, but can also be applied as a net-like layer. The use of a net-like layer reduces the quantity of the polymers required and allows for the transparency of the container.

[0019] A preferred embodiment makes provision for the polymers to be applied as a translucent coating. Such a coating allows for the identifiability of the degree of filling of the container, even if the container has been completely covered by a paint coating.

[0020] Positive results have been achieved with polymers which derive from the group of the conjugated chain molecules, such as the polyanilines. Also especially well-suited are doped polymers or semi-conductor materials, such as are offered for sale, for example, under the trade name Minatec®.

[0021] Good chemical resistance combined with a specific surface resistance in the range from 10³ to 10 Ω meter of the application paint can be achieved by pure tin oxide being rendered a semi-conductor by way of specific doping with antimony oxide. The doping leads to the fact that free-moving electrons are available in the crystal lattice as early as at room temperature. These allow the polymer coating to transport charges, and for the conductive strip to be occupied by electrons. Chemical resistance to acids and lyes and organic solvents is achieved alone or by varying with polyaniline.

[0022] According to another aspect of the present invention, in a method for the manufacture of a transport packing, a surface of a transport packing is subjected to a flame treatment or corona treatment, and the plastic packing is sprayed with a material containing electrically conductive polymers.

[0023] The flame treatment or the corona treatment ensures that the coating applied as paint achieved good adherence to the plastic surface, and that a uniformly thin paint coating can be applied. To do this, spraying is proposed in particular, since by means of this transport packings of this nature can be treated rapidly and uniformly even in industrial operation.

[0024] It is to advantage if the sprayed transport packing is arranged in a metal cage. The metal cage can be earthed in a simple manner, and it ensures that an electrically conductive connection is achieved between the paint coating featuring the electrically conductive polymers and the earthing arrangement. In addition to this, the metal cage also provides a mechanical protection for the transport packing.

BRIEF DESCRIPTION OF THE DRAWING

[0025] Other features and advantages of the present invention will be more readily apparent upon reading the following description of currently preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which FIG. 1 shows a three-dimensional view of a pallet container according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0026] Turning now to FIG. 1, there is shown a three-dimensional view of a pallet container according to the present invention, generally designated by reference numeral 1. The pallet container 1 is referred to as an intermediate bulk container (IBC), which serves for example as a 1,000 liter plastic container for the transport of materials, including inflammable materials. The invention is not, however, restricted to such pallet containers, but also related to plastic drums, canisters made of plastic such as polyethylene and propylene and open packings, especially for substances subject to the risk of explosion.

[0027] The pallet holder 1 includes a plastic bladder 2 and a pallet 3. The plastic bladder 2 in the present case is made of HDPE and the pallet 3 of wood. Metallic pallets are, however, especially well-suited, since they facilitate the earthing of the container. The plastic bladder 2 of the transport packing 1 has a cover 5 in its upper side 4. This cover 5 is manufactured from electrically conductive material or includes electrically conductive polymers. In this context, the conductive surface of the plastic cover 5 is to be formed in such a way that it comes into contact with the surface of the plastic bladder 2, in order to be earthed by it. On the underside 6 of the plastic bladder 2 an outlet 7 is provided, which allows for the filling and in particular the emptying of the container.

[0028] The plastic bladder 2 of the transport packing 1 includes on its outside a paint coating 8, which contains electrically conductive polymers. The paint coating is translucent and slightly greenish in colour, and so allows for the filling level of the container to be identified from the outside. Arranged around the plastic bladder 2 is a metal cage 9, which is formed from vertical struts 10 and horizontal struts 11 and 12. This metal cage 9 holds the plastic bladder 2 firmly to the pallet 3, and can be provided with an earthing arrangement (not shown).

[0029] In the event of a static discharge from the plastic bladder 2, the charge is conducted from the surface of the plastic bladder through the electrically conductive polymers of the paint layer applied until it comes in contact with the metal cage 9. The charge is then conducted away over the metal cage 9, since the metal cage 9 is provided with an earthing arrangement. The cover 5 and the drain tap 7 are either connected in an electrically conductive manner to the outer surface of the plastic bladder 2 or are in direct contact with the metal cage 9, in order to allow for an electrical discharge in these areas as well.

[0030] The paint applied, with electrically conductive polymers, allows for a specific resistance to be created of less than 10³ Ohm×meter, and therefore guarantees the reliable conducting of electrostatic charges. The paint applied further has the advantage that it increases the UV protection, which has a particularly advantageous effect on the filling material.

[0031] By varying the proportion of the conjugated chain molecules in the application paint, the specific surface resistances can be adjusted from 10³ to 10⁶ Ohm×meter.

[0032] While the invention has been illustrated and described as embodied in a transport packing made of plastic and method for the manufacture of a transport packing, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. The embodiments were chosen and described in order to best explain the principles of the invention and practical application to thereby enable a person skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated.

[0033] What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims and their equivalents. 

What is claimed is:
 1. A transport packing, comprising a body made of plastic and including an electrically conductive polymer.
 2. The transport packing of claim 1, wherein the body is a stable hollow body.
 3. The transport packing of claim 1, wherein the body has a volume of more than 450 liters.
 4. The transport packing of claim 1, wherein the body is made of polyethylene.
 5. The transport packing of claim 1, wherein the body has a seam point.
 6. The transport packing of claim 1, wherein the polymer is applied to the body in the form of a paint.
 7. The transport packing of claim 1, wherein the polymer is applied to an outer surface of the body.
 8. The transport packing of claim 1, wherein the polymer is applied as a net-like layer.
 9. The transport packing of claim 1, wherein the polymer is applied as translucent layer.
 10. The transport packing of claim 1, wherein the polymer is selected from the group consisting of doped polymer and semiconductive material.
 11. A method for making a transport packing, comprising the steps of: subjecting a surface of a plastic packing to a process selected from the group consisting of flame treatment and corona treatment; and spraying the plastic packing with a material containing an electrically conductive polymer.
 12. The method of claim 11, wherein the sprayed plastic packing is arranged in a metal cage. 